DH is an ex - traffic cop so I asked him.
It's a myth that speed cameras etc bring in revenue. It goes to a centralized pot along with other court fines etc and doesn't begin to cover the cost of policing the roads. It definitely does not go to the police force.
The focus is on the fatal -5 (speeding, distraction, drink & drugs, not wearing a seat belt & careless driving) as they are the most common factors in fatal collisions & serious injuries.
Middle lane hogging can come under careless driving but is much less likely to be a factor in a fatal collision.
They focus on the things which are shown to be the biggest risks to life - speed being by far the biggest factor, followed by drink & drugs & mobile phone use. This is based on very thorough investigations which takes place following a serious or fatal collision where they look into every factor that contributed.
They use many methods to prevent & detect offences on motorways including patrols (they even own an HGV so they can spot phone use among HGV drivers), technology eg cameras & investigation work following serious collisions.
Lane hogging & more dangerous problems eg dangerous overtaking, undertaking etc are more difficult to take to court from the limited evidence of fixed cameras.
Funding for specialist policing has been cut to the bone in recent years & so there is very little resources to tackle problems & most forces can only look at the biggest causes of death - speed, drink/drugs & mobile phones.
He also highlighted that there is a portal for members of the public to report dangerous driving captured on dashcam - it's caused Nextbase or you can go to your local forces 'report online' tool. If there is sufficient evidence in the dashcam footage the police can take action eg points, fine, warning letter.